A cellular wireless network typically includes a number of cell sites having base stations that are configured to provide wireless coverage in which user equipment devices (UEs) such as cell phones, tablet computers, machine-type-communication devices, tracking devices, embedded wireless modules, and/or other wirelessly equipped communication devices (whether or not user operated) can operate. Further, each base station could be coupled with a core network that provides connectivity with various application servers and/or transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the cellular network could engage in air interface communication with a base station and could thereby communicate via the base station with various application servers and other entities.
Such a network could operate in accordance with a particular radio access technology (RAT), with communications from the base stations to UEs defining a downlink or forward link and communications from the UEs to the base stations defining an uplink or reverse link.
Over the years, the industry has embraced various generations of RATs, in a continuous effort to increase available data rate and quality of service for end users. These generations have ranged from “1G,” which used simple analog frequency modulation to facilitate basic voice-call service, to “4G”—such as Long Term Evolution (LTE), which now facilitates mobile broadband service using technologies such as orthogonal frequency division multiplexing (OFDM) and multiple input multiple output (MIMO). And most recently, the industry is now exploring developments in “5G” and particularly “5G NR” (5G New Radio), which may use a scalable OFDM air interface, advanced channel coding, massive MIMO, beamforming, and/or other features, to support higher data rates and countless applications, such as mission-critical services, enhanced mobile broadband, and massive Internet of Things (IoT).
In accordance with the RAT, each coverage area could operate on one or more carriers, each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), with a single frequency channel multiplexed over time between downlink and uplink use. Further, on the downlink and uplink, each carrier could be structured to define various physical channels including time-frequency resources for carrying information between the base station and UEs. For example, the air interface could be divided over time into frames, each divided in turn into subframes and timeslots, and the carrier bandwidth (frequency width of the carrier on the downlink and/or uplink) could be divided over frequency into subcarriers, which could be grouped within each timeslot to define physical resource blocks (PRBs) in which the subcarriers can be modulated to carry data.
The base station could then be configured to coordinate use of these air-interface resources on an as-needed basis. For example, when the base station has data to transmit to a UE, the base station could allocate particular downlink air-interface resources to carry that data and could accordingly transmit the data to the UE on the allocated downlink resources. And when a UE has data to transmit to the base station, the UE could transmit to the base station an uplink resource request, the base station could responsively allocate particular uplink air-interface resources to carry the data, and the UE could then transmit the data to the base station on the allocated uplink resources.